Production of human T-cell leukemia (lymphotropic) retrovirus (HTLV-I) envelope protein fragments in bacteria and use in seroepidemiological studies

ABSTRACT

Antigenic proteins may be expressed in bacteria by use of vectors having inserted therein DNA fragments from an envelope gene. The DNA fragments employed in the example are coding sequences found in the HTLV-I envelope gene. The bacteria used was E. coli. The antigenic proteins are useful in identifying antibodies to the organisms from which the DNA fragments were originally obtained.

This application is a continuation of application Ser. No. 07/784,915, filed Oct. 30, 1991, abandoned, which is a divisional of Ser. No. 07/126,007, filed Nov. 27, 1987, abandoned, which is a continuation-in-part of Ser. No. 06/664,972, filed Oct. 26, 1984, abandoned.

BRIEF DESCRIPTION OF THE INVENTION

The synthesis of proteins having antigenic properties of viral envelope proteins in bacteria via recombinant DNA techniques provides many advantages over previous methods of production. The antigens may be produced more rapidly at reduced cost. Furthermore, the antigens produced by the recombinant DNA techniques have a defined structure and are not subject to variation arising from mutation of the virus since the structure of the protein is defined by the input DNA.

While the antigens produced according to the inventive method may differ in secondary structure from proteins or protein fragments that are produced in the virus, the synthetically produced structures were recognized by antibodies that are produced in response to native viral protein. The proteins of the invention are useful as diagnostic tools and, when used as imunogens, will elicit production of antibodies which are reactive with the native virus.

The method of the invention was applied using two DNA fragments from human T-cell leukemia virus subgroup I (HTLV-I) envelope gene. The fragments were inserted into pJLA16 plasmids using polynucleotide linkers. These plasmids containing either of the DNA fragments were introduced into E. coli. The MZ1 strain of E. coli which contains a temperature-sensitive repressor was used as a preferred bacteria. The protein-containing fractions obtained from a lysate of the induced MZ1 cells were recognized by antibodies in sera from HTLV-I infected patients.

BACKGROUND OF THE INVENTION

Antibodies that react with HTLV-I proteins have been found in the sera of adult T-cell leukemia lymphoma (ATL) patients. These antibodies recognize both the gag core antigens and the envelope proteins of the virus. Viral core proteins were readily purified, sequenced, and extensively used in immunoassays; however, progress with the more important viral envelope proteins was slower. A limiting factor, therefore, in the studies of the immune response to these viruses has been the difficulty in isolating the viral envelope proteins in pure form and in quantity.

The proviral DNA of HTLV-I has been cloned Seiki et al., Proc. Natl. Acad. Sci. USA, 79:6899 (1982) and Manzari et al., Proc. Natl. Acad. Sci. USA, 80:1574 (1983)! and sequenced Seiki et al., Proc. Natl. Acad. Sci. USA, 80: 3618 (1983)!. The HTLV-I envelope is expressed by placing it into the pJLA16 derivative Lautenberger et al., Gene Anal. Techniques, 1:63-66 (1984)! of plasmid pJL6 Lautenberger et al., Gene, 23:75 (1983)!. This plasmid contains the 13 amino-terminal codons of the bacteriophage lambda cII gene placed under the transcriptional control of the well-regulated phage lambda p_(L) promoter. This plasmid is known and has been successfully used to express sequences from myc, myb, and ras oncogenes Lautenberger et al., Gene, 23:75 (1983) and Lautenberger et al., in Gene Amplification and Analysis, Volume 3, Expression of Cloned Genes in Prokaryotic and Eukaryotic Cells, Papas et al (eds), Elsevier, N.Y./Amsterdam, pp. 147-174 (1983).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Individual fragments of the HTLV envelope gene inserted into plasmid vector pJLA by the use of polynucleotide linkers.

FIG. 2: Uninduced (U) and induced (I) E. coli cell extracts of expression plasmid vectors in gels stained for total protein.

FIG. 3: Western blot of HTLV envelope products produced in bacteria expressing the pKS400-encoded polypeptide. Prominent 15 kd band indicates immunoreactivity of the bacterial envelope product with sera from HTLV infected patients.

DETAILED DESCRIPTION OF THE INVENTION

Initial attempts to express the entire HTLV-I envelope were unsuccessful, possibly because this protein can interact with the bacterial cell membrane in such a way as to be toxic to the cell. Therefore, individual fragments coding for specific regions of the envelope were inserted into pJLA6 by use of polynucleotide linkers (FIG. 1).

The HTLV-I env gene codes for a glycoprotein (gp61) of molecular weight 61,000 that is cleaved into the molecular weight 46,000 exterior glycoprotein (gp46) and the molecular weight 21,000 trans membrane protein (gp21E). The precise site of proteolytic cleavage has been determined by locating radiolabeled valine residues with respect to the amino terminal end of gp21. The cleavage of the env gene precursor is adjacent to the residues Arg-Arg that also occur next to the proteolytic cleavage sites in the bovine leukemia virus (BLV) and mouse mammary tumor virus (MMTV) env precursor. Since the BamHI site that separates the inserted fragments is close to the region coding for proteolytic cleavage site that separates gp46 from p21E, the protein from pKS300 contains sequences corresponding to the carboxy-terminal portion of gp46 and the protein from pKS400 predominantly consists of sequences from p21E. Based on DNA sequence data of the envelope gene fragments utilized in the example, the calculated molecular sizes of the pKS300 and pKS400 proteins are 12.84 Kd and 15.88 Kd, respectively. These sizes include the 1.56 Kd coding sequence contributed by the amino terminal codons of the lambda cII gene. The observed molecular weights of both proteins on SDS-polyacrylamide gels are consistent with those calculated for a 321 base pair (pKS300 insert) and 397 base pair. (pKS400 insert) coding sequences.

EXAMPLE 1

Construction of plasmids pKS300 and pKS400. Plasmid pHTLV-I HX-CR was obtained by subcloning the 5.7 kb Hind III-XbaI fragment of lambda CR1 Manzari et al., Proc. Natl. Acad. Sci. USA, 79:6899 (1982)! that contained envelope, pX, and LTR sequences. Lambda CR1 contained integrated HTLV-I proviral DNA from mycosis fungoides patient CR. pHTLV-I HX-CR DNA was digested. XhoI and BamHI and the 300 bp and 400 bp fragments containing the env sequences were isolated from an agarose gel. The termini of these fragments were converted to blunt ends by the action of Klenow fragment E. coli DNA polymerase I and Hind III linkers were attached. Excess linkers were removed by digestion with Hind III and reisolation of the fragments from agarose gels. The pJLA16 Lautenberger et al., Gene Anal. Techniques, 1:63-66 (1984)! vector DNA was cleaved with Hind III and the ends were dephosphorylated by the action of calf intestinal phosphatase. The dephosphorylated vector DNA was ligated to the fragment DNAs and introduced into DC646 cells by transformation using ampicillin selection. Plasmids containing inserts were identified by hybridization of colonies transferred to nitrocellulose with radiolabelled fragment produced by nick-translation of fragment DNA using alpha-³² P!dCTP. For protein expression experiments, the plasmids were transferred into a prokaryote host such as by transferring into E. coli (strain MZ1) provided by M. Zuber and D. Court.

The MZ1 strain contains a partial lambda prophage bearing the mutant cI857 temperature-sensitive repressor. At 32° C. the repressor is active and p_(L) promoter on the plasmid is repressed. At 42° C. the repressor is inactive and the p_(L) promoter is induced, allowing high level expression of genes under its transcriptional control. When lysogens carrying either of the two plasmids containing different portions of the HTLV-I envelope gene (cf. ante) were grown at 32° C. and induced by shifting the temperature to 42° C., prominent bands were observed that were not found in uninduced cells or in induced cells containing the pJL6 vector alone (FIG. 2).

EXAMPLE 2 Expression of the HTLV-I envelope gene in E. coli

(a) Radiolabeling of bacterial cell proteins. E. coli MZ1 cells were grown at 32° C. induced by shifting the temperature to 41° C., labeled with ³⁵ S!-cysteine and lysed. Proteins were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and visualized by autoradiography.

(b) Uninduced (U) and induced (I) cell extracts of expression plasmid vectors were observed in gels stained for total protein. See FIG. 2 showing Lane 1, pJL6 vector without insert; Lane 2, pJLcII ras; Lane 3, pKS300; Lane 4, pKS400.1; Lane 5, pKS400.2; Lane 6,400 bp fragment in wrong orientation.

In order to see if such antibodies can recognize a bacterially synthesized envelope product, a lysate of induced MZl pKS400! cells containing this protein was fractionated by SDS-polyacrylamide gel electrophoresis and transferred to nitrocellulose sheets by electrophoretic (Western) blotting. Strips containing the transferred proteins were reacted with diluted human serum and antigen-antibody complexes formed were detected by incubation of the strips with ¹²⁵ I-labeled Staphlococcus aureus protein A followed by autoradiography. As shown in FIG. 3, prominent bands corresponding to reaction of antibody to the 15 Kd bacterial envelope product could readily be observed when the serum used was from patients with HTLV-I associated ATL or from HTLV-I antigen (+) individuals. No such reaction bands were observed with sera from healthy control individuals. This procedure was used to screen a group of 28 coded sera. Antibodies that recognized the bacterially synthesized HTLV-I envelope protein sequences were found in all sera that had been shown to have anti-HTLV-I antibodies by ELISA assay using disrupted virions as antigen (Table 1). Thus, a method is formulated for serologically testing for the presence in human sera of antibodies directed against HTLV-I or HTLV-II. None of the normal control sera were found to have reacting antibodies. Antibodies from a patient (Mo) with a hairy cell leukemia, whose disease is associated with HTLV-II, strongly reacted to the protein coded for in pKS400 indicating that there is a high degree of relatedness between the p21E region of HTLV-I and HTLV-II.

EXAMPLE 3 Recognition of bacterial synthesized HTLV-I envelope protein by antibodies in human serum

MZ1 pKS400! cells were grown at 32° C., induced at 42° C., and lysed in the presence of 1% SDS-0.1% beta-mercaptoethanol. Protein in the extracts were resolved by SDS-PAGE and electrophoretically transferred to nitrocellulose paper by the "Western blot" procedure. After transfer, filters were air dried and soaked in TBS-NDM (50 mM Tris-HCl, pH 7.5, 500 mM NaCl, 3% Nonfat Dry Milk). The filters were incubated overnight at room temperature in TBS-NDM plus 1/77 volume human serum as indicated below. Filters were then washed with TBS-NDM for 30 min and then incubated with 10⁵ cpm ¹²⁵ I!-protein (NEN). The filter was then washed with TBS-NDM and finally with TBS. The filters were air dried and protein bands reacting with antibody were visualized by autoradiography (see FIG. 3). The sera used were: (1) American ATL patient; (2) T-cell hairy cell leukemia patient Mo (Ref. 4); (3) Healthy normal

                  TABLE 1     ______________________________________     Presence of Antibodies Recognizing Bacterially     Synthesized HTLV-I Envelope in Human Sera                    HTLV-I or                    HTLV-II +/- Number   Number     Status         (by ELISA)  Tested   Positive     ______________________________________     Clinically normal                    +           2        2/2     heterosexual   -           8        0/8     Clinically normal                    -           5        0/5     homosexual     AIDS patients  +           2        2/2                    -           2        0/2     ATL patients   +           5        5/5     Mycosis fungoides patient                    +           1        1/1     Hairy cell leukemia                    +           1        1/1     patient Mo (HTLV-I +     patient)     Lymphadenopathy                    -           2        0/2     syndrome patients     ______________________________________      (4) Healthy normal; (5) Healthy normal; (6) Healthy relative of ATL      patient; (7) Healthy normal; (8) Japanese ATL patient; (9) AIDS patients      found to be HTLV-II (+) by ELISA (disrupted virus antigen); (10) AIDS      patient found to be HTLV-I (+) by ELISA (disrupted virus antigen); (11)      Healthy normal; (12) American ATL patient; (13) Mycosis fungoides patient;      (14) Healthy normal found to be HTLV-I (+) by ELISA (disrupted virus      antigen). Uninduced and induced extracts pKS400.2 reacted with patients MJ      serum (HTLV-I positive by ELISA).

Since the bacterially synthesized HTLV-I env protein was recognized by antibodies present in sera from AIDS patients, it was also of interest to show that this assay can be utilized to screen for a more distantly related subgroup, namely, HTLV-III (known now as HIV, causative agent of AIDS). Therefore, a number of sera samples of AIDS patients, some of which were also sero-positive for HTLV-I, were examined.

The sera from all positive AIDS patients which reacted with HTLV-I in ELISA contained antibodies that recognized the bacterial synthesized HTLV-I env protein. None of the sera from AIDS patients that were HTLV-I negative contained antibodies that reacted with the bacterial protein. Since antibodies that react with HTLV-III proteins can be found in the serum of greater than 90% of AIDS patients, this result indicates that there is little or no cross reaction between the carboxy-terminal portion of the envelope proteins of HTLV-I and HTLV-III. pKS300 and pKS400 have been deposited with the American Type Culture Collection (ATCC), at 12301 Parklawn Drive, Rockville, Md. 20852. pKS300 has the ATCC designation of 39902, and pKS400 has the ATCC designation of 39903. 

What is claimed is:
 1. A polypeptide having the sequence of amino acids encoded by an isolated HTLV-I envelope DNA fragment contained in plasmid pKS300 having ATCC Accession No. 39902, said envelope polypeptide being immunologically reactive with anti-envelope antibodies in sera from HTLV-I infected individuals.
 2. The polypeptide according to claim 1, said polypeptide having carboxy terminal amino acid sequences of HTLV-I exterior glycoprotein gp46.
 3. A composition of matter comprising the polypeptide according to claim 1 bound to a solid support.
 4. The polypeptide according to claim 1 or claim 2 produced by expressing the pSK300 plasmid in E. coli.
 5. The polypeptide according to claim 4, wherein said E. coli is E. coli strain MZ1.
 6. A polypeptide having the sequence of amino acids encoded by an isolated HTLV-I envelope gene fragment resulting from XhoI and BamHI restriction endonuclease digestion of cloned HTLV-I DNA containing the HTLV-I envelope gene, said polypeptide being immunologically reactive with anti-envelope antibodies present in sera from HTLV-I infected individuals.
 7. A method of detecting antibodies reactive with HTLV-I envelope proteins in a sample comprising:a) contacting the sample with the polypeptide according to claim 1 under conditions such that the antibodies reactive with the HTLV-I proteins present in the sample can immunologically bind to the polypeptide to form a complex; and b) detecting the presence of the complex.
 8. A method of detecting antibodies reactive with HTLV-I envelope proteins in a sample comprising:a) contacting the sample with the polypeptide according to claim 6 under conditions such that antibodies reactive with HTLV-I proteins present in the sample can immunologically bind to the polypeptide to form a complex; and b) detecting the presence of the complex.
 9. A polypeptide having the sequence of amino acids encoded by an isolated HTLV-I envelope DNA fragment contained in plasmid pKS400 having ATCC Accession No. 39903, said envelope polypeptide being immunologically reactive with anti-envelope antibodies in sera from HTLV-I or HTLV-II infected individuals.
 10. The polypeptide according to claim 9, said polypeptide having the transmembrane amino acid sequences of HTLV-I protein p21E.
 11. A composition of matter comprising the polypeptide according to claim 9 bound to a solid support.
 12. A fusion protein consisting essentially of the polypeptide according to any one of claims 1, 9, or 6 fused to a sequence of amino acids unrelated to the HTLV-I envelope amino acid sequence.
 13. A method of detecting antibodies reactive with HTLV-I or II envelope proteins in a sample comprising:a) contacting the sample with the polypeptide according to claim 9 under conditions such that antibodies reactive with the HTLV proteins present in the sample can immunologically bind to the polypeptide to form a complex; and b) detecting the presence of the complex.
 14. The polypeptide according to claim 9 or claim 10 produced by expressing the pSK400 plasmid in E. coli.
 15. The polypeptide according to claim 14, wherein said E. coli is E. coli strain MZ1. 